To dream of knocking represents you or someone else that wants to be noticed. It may also reflect a situation that is forcing you to notice it's importance.
To dream of a loud knock at the door represents feelings of seriousness about some person or area of your life demanding acknowledgement. Feelings about a problem that can't be ignored anymore. Feeling that someone is very angry with you while you prefer to ignore them. Feeling nervous about confronting a problem. Feeling that someone is testing your nerves.